CHICAGO -- At the Famous Footwear outlet here on Madison Street, merchandise was missing left and right. Nailing the culprits wasn't easy. Some of them were the store's own employees.

Familiar with the gaps in store security, the chain's workers knew how to scam the system. One ruse: If a friend brought a $50 pair of Skechers sneakers to the checkout counter, a dishonest cashier might scan a $2 bottle of shoe polish, just to make a...